How do you target a new player with a command on Minecraft 1.19.3?

Question

I'm currently writing a datapack and want to have a message send only once to a player when they join the server for the first time.

I have a rough idea of how I could use scores to say who isn't new, but I can't figure out how to target someone when they join.

Here's a quick example of my idea:

/execute unless entity @a[score={joined=1..}] run msg @[<Part I can't figure out>] Welcome
/execute unless entity @a[score={joined=1..}] run scoreboard player add @[<Part I can't figure out>] joined 1

It's just a rough example to show what part I'm talking about, so don't come at me if the syntax is wrong.

Answer 1

I found an answer, I didn't realize that when selecting a target, you can use =! to say "not equal to". So when you would type @[tag=!<your tag here>] to target the user then give them the tag afterwards.

Answer 2

You can use @s selector:

execute as @a at @s unless entity @s[joined=1..] run msg @s Welcome
execute as @a at @s unless entity @s[joined=1..] run scoreboard player add @s joined 1